Temperature and Density Dependence of the Transport Properties of the Ionic Liquid Triethylpentylphosphonium Bis(trifluoromethanesulfonyl)amide, [P222,5][Tf2N

Abstract

Viscosities (η), conductivities (κ, Λ), and ion self-diffusion coefficients (DSi) for triethylpentylphosphonium bis(trifluoromethanesulfonyl)amide, ([P222,5][Tf2N]), have been measured as a function of temperature and pressure in the ranges ([273–363] K, 243 MPa max), ([273–353] K, 251 MPa max), and (298–363 K, 225 MPa max), respectively. pVT data are also reported from (298 to 353) K to 50 MPa. The ratio of the ion self-diffusion coefficients is constant, independent of temperature and pressure. The results are discussed using velocity correlation, distinct diffusion, and resistance coefficients, and the Stokes–Einstein–Sutherland (SES: relating DSi and η) and Nernst–Einstein equations (NE: relating Λ and DSi). As is usual for ionic liquids the SES and NE plots for high-pressure isotherms and the atmospheric pressure isobar overlap quantitatively, that is the self-diffusion and distinct diffusion coefficients, and the molar conductivity, are functions of the viscosity. This can be used for the interpolat...